Telegraph concentration board spare communication circuit



July 29, 1952 M. R. PURv|s 2,605,347

TELEGRAPH CONCENTRATION BOARD SPARE COMMUNICATION CIRCUIT Filed April 29, 1949 3 Sheets-Sheet l ATTORNEY July-29, Ml R' PURV|5 TELEGRAPH CONCENTRATION BOARD SPARE COMMUNICATION CIRCUIT Filed April 29, 1949 v :s sheets-sheet 2 y C v a C n u A 7' TORNE V M. R. PuRvls July 29, 1952 TELEGRAPH CONCENTRATION BOARD SPARE COMMUNICATION CIRCUIT Filed April 29. 1949 5 Sheets-Sheet 5 /NVE/vroR BV MR. PURV/S Arrow/EV m. .gk

Patented Julyl 29, 1,952

,z TELEGRAPH CONCENTRATION BOARDk SPARE COMMUNICATION CIRCUIT Matthew R. Purvis, Fanwood, N. J., assigner to rvBell Y Telephone Laboratories, Incorporated,l VNew York, N. Y. a corporation of New York .in Application April 29, 19d?, Serial No.`90,5`14

(C1. ris-2) Y i a w 3 Claims.

This invention relates to telegraph systems and more particularly tou telegraph systems wherein private branch lines are associated together in local, statewide;r or nationwide networks on a semipermanent basis as distinguished from Ya telegraph exchange switching system, which latter resemblesl ,al telephone exchange system in function. 4 Such networks may now be administered at so-called telegraph service boards where telegraph kline Vand loop concentration groups are built up and connected by means of lines to other concentration groups in other cities as required forthe needs of various patrons such as large corporations. Such concentration groups may remainvundisturbed for relatively long intervalssuch as for days or weeks at -a time. By meansvof a special repeater sys-` tem known as a hub-type repeaterin-which the individual repeater units through which the lines and loops vare interconnected at each concentration .group point do not require adjustment to compensate fOr diifering line. or 4loop Acharacteristics, each concentration group is arranged so that linesy to other concentration groups at distant cities as well as local circuits may be added, subtracted or substituted directly by van operator at the service board instead of requiring the services of maintenance men or repeater adjusters whenever a change is necessary as formerly. This results in more eicient operation. In order to/permit this tobe done it is necessary to add an individual repeater component of the hub-type repeater to each line or loop in a concentration group. Telegraph service...board operation is described in Patents 2,349,586 and 2,413,686 granted May 23, 1944 and January '7, 1947, respectively, to A. R. Bonorden et al. The circuits of the present invention are designed for operation in service generally resembling that described in the foregoing patents.

An object of this invention is the improvement of arrangements for terminating spare telegraph branch lines which may at times be employed commercially as part of a network ina telegraph The arrangements described hereinfprovide for the connection of an answering jack circuit to veach terminal of a spare line dual facility which may serve as part of a network or as a maintenance line andwhich isv known in the art as a communication spare facility, commonly designated a ESPfacility.' Thus, at each end, such a facility invaddition toits concentration `jack circuit isI alsoterminated in an answering jack circuit. As thus arranged such a facility may serve' at times as apart of a commercial network and at other times as Aa maintenance facility. This flexibility tends to reduce the cost. v i

First, to describe the operation' of the circuits in general terms, in the idle condition the line facility is marking in both directions. i An attendant originates a call by connecting the v manual telegraph cord circuit to the communiservice .board attendants for maintenance and other purposes.

Anotherv object of thisinvention is the pro.

or'as a spare communication channel, to another oice over a second similarbranch telegraph line,

the line.

andautomatically signaling the calledl office over.

over the line facility and causes the answering lamp to light'at the telegraph service 'board in the calleddistant oce where the call is Vanswered vwith -a manual telegraph cordv circuit. Each manualtelegraph cord circuit includes a telegraph key and sounder. The two attendants may communicate over the single vline facility and if the call is ultimately destined for another more distant telegraph service board, so that a tandem connection is required, the answering attendant takes the calling end vof a different cord circuit which does not include a telegraph key and sounder, namely a telegraph connecting cord circuit 'and connects'it tothe answering jack circuit of a communication spare `facility that terminates in the more distant'c'alled office. This causes a spacing signalto' be'sent over the secondjcommunication spare` facility.` The attendant at `ther through or .intermediate point immediately disconnects vthe manual' telegraph cordfcircuit from the answering jack circuit. of the incoming `line fromhthejcalling office and replaces it with` the answering cord ofthev tele-a graph connecting cord circuit. This stops the space or calling signal that Wasstarted by oo nnecting the callingV cord of the., telegraph con*- necting cord circuitto'the answering jack circuit of they f communication if' spare facility jfextending to the more'distantofce'. The attendant at the more'distant Vcalled'oflice-answers with a manual telegraph'A cordV circuit" and communication bedem connection sends a 20-cycle ringing signal.. which causes a supervisory lampin'the telegraph i connecting cord circuit, at the intermediate oflice to light. This noties the attendant.V at the .in-f termediate oflice that the telegraph. connectingVY cord circuit should be disconnected from the 4 extinguished. Condenser |01 is charged to a positive potential. ing, relay R operates to space and connects negative battery |02 through resistance |06 to the grid network consisting of resistances |08, |09 and |32 and condenser |01. Condenser |01 begins to lose itsfpositive cliargeand the fallin potential of thevcondenser` is applied to the grid of the tube through resistance |09. After the space signal has persisted for a predetermined interval, which maybe assumed to be in the order ofv one'second,the"grid will have lost its positive potential and'b'ecome charged suilciently negative that'ftub'ell will stop conducting and cause relay A tobe. released. The rate at which condenser" |01 is ydischarged and charged is regulated by properly proportioning the values of the reanswering jack circuits of theV two communica?.

tion spare facilities extending toward thecallirig` Fig. 2 represents the telegraph connecting cord circuit at an intermediate office;

Fig. 4 representsv :a manual telegraph cord circuit and Fig. 5 is a schematic diagram of captioned rectangles showing the relationship of Figs. 1 to 4 in a typical arrangement'.

Communication spare (KSP) terminating circuit Figs. 1 and 3 In each o f Figs. 1y and 3 relays R and S, resistances |06, |04 and |05"and batteries |0|, |02 and |03 are. part ofthe line repeater which terminates in the LEGS and KSP jacks. The LEGS jack isA part of the concentration jack circuit and serves principally as a means for patching the line facility out as a spareso thatit may be employed commercially in la patrons network. The KSP terminating circuit provides supervisory arrangements for originating and completing calls over spare line telegraph facilities, primarily for maintenance service between service boards.

The terminating circuit is described las follows: In the idle condition the facility, which is full duplex, is transmitting a mark in both directions. A mark is transmitted outward in Figs. 1 and 3 because there is no current flow from battery |03 through the line winding of relay S and resistance |05, as there is no connection at the KSP jacks and the circuits are open thereat. Current ilows from battery |03 through the bias winding of relay S and resistancel|04 to ground and this' current causes the armature of relay S to operate to. marking and send a mark over the line. An incoming mark representing the idle condition causes relay R to be operated to marking and this connects positive battery |0| Via the armature of rt'elay R, resistance |06, tip springs of the LEGS a'nd KSP jacks,l resistances |08 and |09 to the grid of the tube Since the grid is more positive than the cathode of tube the tube will conduct and hold relay A operated by current 'flow through the winding of the relay and resistanceV |4 to positive battery ||5. When relay A is'operated, the ANS lamp circuit is open at Contact |39 and the4 lamp is' sistancesin the grid network. When relay A releases; contact |39 closes and lights lamp ANS over an obvious circuit, to indicate the presence of an incoming call. Thefrelease of relay A also closes a circuit through contact |40gof relay SA and contact |4| of relay A in seriesV that short-J circuits the winding of relayA. 1 Relay A is there by prevented from reoperatingfwhenl theincom-v ing space signal is superseded'by. a mark and tube again conducts. VALamp. ANS remains lighted until the local attendant answers by connecting the telegraph cord, TLG30 in the manua1 telegraph cord circuitper Fig. 4 to the KSP jack. At that time relay SA operates from current produced by battery inthe sleeve circuit ofA the telegraph cord circuit.V Y Operation of the manual telegraph cord circuit will be described later. Operation'of relay SA opens the short'- circuiting path which is parallel-with theV It falso connects ground,

Telegraph connecting cord circuit. Fig. 2

Ifn an attendanty should answer v.an incoming call received over the line facility terminated in Fig. 1, using the manualtelegraph cordv circuit per Fig. 4, only to vfindy that his o i'lice to be a through or intermediate point" in a built-up connection to anotherl oice, heproceeds to complete the connection as'ncw described-, VThis description applies at any threughjpoin't' in the built-up connection. Y Y

The CALL cordV of a telegraph connecting 'co'rrd circuit p er Fig. 2 is connected tothe KSP jack ci a line facility such as Fig;l '3 whichvit will be assumed extends to thecalledtoliice. `1Relay S of the CALL cord is releasedN since the circuit through its winding is operlfat the sleeve of the answeringV 'cord ANS which' is disconnectedat this time. The ring andsleeveof the CALL cord will be interconnected through contact |42 and ground will be connected through the winding of relay SA of the KSP facility, through resistance ||3 to the sleeve of the'fjack, fromth'e sleeve through contact |42 tothe ring ,Of the cord cir? cuit, through the ringj contacts' o`f jacks KSP and LEGS, resistance |05'Eand throughl vtheV line wind,- ing of relayS of ther facility to batt/ery |03. AThis will causeY relay S to operate 'to spacing and'theref by send a space over the facility'to the ,distarli'gV When a call signal is incomoice asV al call signal.' After approximately two seconds,- the attendant disconnectsthe manual telegraph vcord circuit 4per Fig. llrf'rom the KSP jack'of ther facility of Fig. 1 and connects the ANS cord of the telegraph connecting cord 'circuit perA Fig.- 2 to this ljack. Relay S of the cord circuit `operates due to current flow from battery |3I,vthroughthe relay winding over the sleeve of cord ANS, sleeve of jack YKSP, Fig. 1-, resistance I I3 and the winding of relay SA to ground. Relay SA of Fig. l-therefore operates at this time. With the operation of relay S of the cord circuit the connectionbetween the ring and sleeve of the CALLv cord is opened at contact |42 and transmission of the Vspace signal over the facility of Fig. l3 is-Vinterrupted. The attendant at the called cnice answers the call and communication begins.

Transmission of signals from facility I to facility 3 is from the armature of relay R, facility through resistance |6, tip springs of jacks LEGS and KSP, tip conductor of cord ANS, resistance A| I8, ring of cord CALL, into facility 3, through lring springs of jacks KSP and LEGS, resistance |95 and the line winding of relay S to battery |53. 'I'ransmissionl from facility 3 to facility may be traced in the reverse direction and the signals pass through resistance I I9 of the telegraph connecting cord circuit. After the patch has been completed between the facilities land 3 of Figs. 1 and 3, relay SA of facility will be held operated by current, which flows from ground through the winding of relay SA, resistance |I3, sleeve of jack'KSP, sleeve of cord ANS andthe winding of relay S to battery'IG-BI.A Relay A in Fig. l will thus be held operated and the ANS lamp will remain extinguished. In'the case of facility 3 operation of the tip spring contacts of jack KSP disconnects the grid network of tube from the RL lead. Tube in line facility 3 will be held conducting by positive battery ||0 applied through resistances |32 and |59 to its grid and in the conducting condition the tubewll hold relay A operated. Lamp ANS of facility 3 will therefore be maintained extinguished. A

The telegraph connecting cord circuit, Fig. 2, includes a disconnect signaling feature which reduces the holding time on the KSP trunks which terminate in Figs. l and 3. This feature requires that either the calling or called telegraph service board attendant send a 20-cycle ringing signal upon completion of communication. This ringing signal causes the SU'PV lamp associated with the telegraph connecting cord circuit at each intermediate point to light, whether there be one or several Figs. 2 in the tandem connection, as an indication that the cord'should be disconnected immediately to release the KSP trunks. The 20- cycle ringing signal is sent from the manual telegraph cord circuit at either the calling or called terminal. Operationv of the disconnect signaling feature will'now be described.

A ringing signal transmitted by a manual tele' graph cord circuit per Fig. 4 connected to a KSP jack, ateither terminal, applies i105 volts at a 20cycle frequency to the ring conductor of the KSP jack, at the terminal, in a manner to be describedyand this causes current to flow in the line winding of the S relay of the facility. Relay S WillV respond to the voltage alternations of l2()- cycle frequency and transmit alternate vmark and space pulses over the KSP facility to actuate the armature of thereceiving relay R at the associated opposite end. of the facility. If the ringing signal'is transmitted by the'calling office the' 6. alternateA marking and spacing signals will enter all telegraph connecting cord circuits per Fig. 2 in series in the tandem connection Via the tip of the ANS cord. Part Vof the signaling current entering the tipof the ANS c 'ord will pass through winding |45 of relay L. andzcause thisrelay to vibrate. The rest will passthrough resistance I I8, the ringsprings of jacks KSP-and LEGS, resistance |05, the line winding of relay S to battery |03. Relay S, Fig. 3, will also respond to the ringing signals. Likewise if the ringing signals are transmitted fromthe called oflce they will cause the S relay of the associated KSP facility to vibrate and repeat them over the facilities of the built-up connection. Y Alternate marking and spacing signals resulting from the ringing signals will enter the CALL cord tip conductor of every telegraph connecting cord circuit in the built-up connection. Part of the signal current will pass through winding |44 of relay L and the rest will pass through resistance I9 and over the ring of the ANS cord, to operate the S relay of the facility of Fig. 1. In any event relay L will vibrate at 20 cycles y.per second either from current in its upper or lower winding. When the armature of relay L, Fig. 2, engages its left-hand contact, current flows from battery through the right-hand winding of relay R, left-hand contact of relay L, through Condensers |24 and |25 in parallel and the winding of inductance |33y to ground. When the armature of relay L engages its right-hand contact, `current flows from the tuned circuit comprising inductance |33 andv condensers |24 andy |25 in parallel through the right-hand conv tact of relay Land the left-hand winding of relay R. .The direction of the flow of current through each of the windings of relay R alternately is such that itseifect tends to vactuate the armature of relay R, Fig. 2, to engage'with its contact. The capacitance of Condensers |24 and |25 and the inductance of coil |33 are tuned so that when relay L vibrates at 20 cycles per second there is sufficient current flowing in the windings of relay R in Fig. 2 to cause this relay to operate. If relay Lr happens to be responding to telegraph signals or is vibrating at some frequency other than 20 cycles, there will be insufficient current to operate relay R. Relay R will thus be operated only when repeated marking and spacing signals are received at the rate of approximately 20 cycles per second. It is also necessary that these signals continue forv one or more vseconds in order to give relay R time to operate. When relay R operates it closes an obvious circuit to operate relay A which locks up to ground supplied through make contacts |45 and |41 of operated relays S and A. Operation of relay A closes a circuit through contact |48 to light supervisory lamp SUPV which remains lighted until the ANS cord is taken down at which time relay S is released. Prompt'disconnection of the telegraph connecting cord circuit frees the KSP- trunks for immediate use. Condensers 2| and |21 and resistance |29 and |26 serve as spark protection networks for the contacts of relay L. Winding |49 normally biases the armature of relayA L to engage the contact |50 but no current flows in the windings of relay R except while relay L is vibrated.

The manual telegraph cord circuit, Fig. 4, is used for communication purposes between the service board personnel in conjunction with KSP trunk circuits. Operation of this cord circuit in conjunction with KSP trunk circuits will now be 4 is connected to the KSP jack of a spare line facility, such as Fig. 3 for instance, which is terminated in a KSP jack circuit, telegraph cord 'I'LG30I is used. 'Sleeve current flows from ground in the KSP jack circuit, Fig. 3, through the winding of relayY SA, resistance ||3, sleeve of the KSP jack, over the sleeve of telegraph cord TLG30l, Fig. 4, resistance 340, and through the windings of relays B and A to battery 321. This current flow serves to operate, relay SA in the KSP terminating circuit per Fig. 3, but relays B and A of the cordV circuit do not operate because the current is insuflci'entv to operate marginal relayB and is in the wrong direction to operate polar relay A. The manual telegraph cord circuit per Fig. 4 has application to several different kinds of service board jack circuits in addition to those disclosed herein, and itv is the purpose of relays B and A to distinguish between the various jack circuits and arrange the cord circuit per Fig. 4 to function properly with any of the circuits with which it is intended to be associated. Connection of cord TLG to the KSP jack circuit causes the tip and normal jack springs to open and. disconnect the grid network of tube from receiving leg RL. VThe line facility per Fig. 3, the sending relay S of which is sending a mark to the distant oince for the idlel condition, continues to send a mark until the attendant operates the sending telegraph key, SEND 'ITG key, in the telegraph cord circuitper Fig. 4, while leaving telegraph key 302 open, which effects the transmission of a spacing or call signal. The spacing or call signal is transmitted because relay E, Fig. 4, will be held to its left-hand or spacing contact under the influence of current in its lower or biasing winding, over an obvious circuit, while no current flows in its upper winding as contact 355 and key 302 are open. In this condition current will now from negative battery 306, throughthe armature of relay E, resistance 303, closed contacts 350 of key SEND TLG, back contacts 35| of relay Bl, back contacts 352 of relay A2, closed contacts of unoperated key RING, resistance 331, back contacts 353 of relay AI to the ring of cord TLG. From the ring of cord TLG the current flows over the SL lead through resistance |05 and the line winding of relay S in the line repeater to battery |03. This current flow will overcome the effect of the bias current, fiowing from battery |03, through the biasing winding of relay S and resistance |04 to ground, and cause this relay to operate to spacing. A space signal, therefore, will be transmitted over the facility and serve as a call signal. After sending the call signal for several seconds the attendant closes telegraph key 302 to send a mark. This causes current to flow from battery 304 through the top winding of relay E and closed telegraph key 302 to ground and operates relay E to marking. Positive battery 305 replaces negative battery 306 in the circuit traced above. Battery 305 in Fig. 4 now opposes equal battery |03 in Fig. 3 and no current flows in the line winding of relay S. Relay S, therefore, operates to mark-- ing under the influence of current in its biasing winding. The circuit is now ready to receive a response from the. called oflce.

Signals from the called office are repeated by the R relay of the line facility Fig. 3, and pass over the RL lead, through resistance |06, tip springs of jacks LEGS and'KSP, over the tip of the cord circuit Fig. land through resistance 320 to the grid of tube 3|1. Positive Apotential from source |03 vwill also be applied through the ring conductor of the KSP jack and the ring conductor of the cord to the grid of tube 3l'l. As a result the grid of tube 3 l1 is now held positive by connection to battery |03 in the line repeater and battery 305 in the cord circuit. The connection from the ring conductor of the cord to the grid of the tube may be traced from the ring conductor ofthe cord through back contacts 353 of relay Al, resistance 331,n back contacts 351 of relay Al, closed contacts 359 of full duplex-half duplex key FDX--HDX and through resistance 3|9 to the grid. The grid of tube 3 l1 has a, second continuous source of negative potential which is obtained from negative battery 336 through back contacts 36| of relay AI and resistance 3|8. This negative battery branch compensates for the steady positive potential applied by the ring of the cord through resistance 3|9 and causes the grid potential to be centered at the correct potential for the reception of signals from the RL lead of the facility. Signals from the distant ofce will accordingly cause tube 3 1 to conduct for a mark and cut olf for a space. 'The screen grid of tube 3|1 is connected to a potentiometer consisting of positive battery 3 I 6 and resistances 3|5 and 3I4. This potentiometer is adjusted so that a plate current of approximately 30 mils flows from positive battery 301 through resistance 3|3, the line windings of relays RI and R and the plate-cathode circuit of tube 3|1 to ground. With a biasing current of approximately 15 mils flowing through their lower or biasing windings, these relays respond to incoming signals. Relay R is arranged to transmit polar signals through resistance 3|2 to the transmission measuring set which may be connected to the transmission measuring set jack TMS. Relay Rl transmits on a neutral basis through resistance 308. back contacts 36| of relay SI and the winding of sounder SDR of the telegraph set to ground.

The local attendant sends to the distance oice by opening and closing telegraph key 302 which actuates relay E. Relay E transmits over the circuit previously traced and causes relay S in the line repeater to respond and repeat the signals outward over the facility. Current flow through the line winding of relay S is limited to the optimum value by series resistances 303 and 331 in Fig. 4 and resistance |05 in Fig. 3. The receiving element of the telegraph cord circuit responds to outgoing signals and provides local copy. In this case the out going signals are applied to the grid of tube 3l1 via resistance 3| 9 While continuous positive and negative potentials are applied to the grid through resistances 320 and 3|8 respectively. The potential applied through resistance 320 comes from the RL lead of the facility which is marking and that applied through res1stance3 I8 is from negative battery 336. The grid potential of thetube is therefore properly centered for reception of outgoing signals.

Upon completion of communication and before the cord circuit is' disconnected from the KSP Jack, the attendant may-wish to send a 20-cycle ringing signal over the KSP facilities to notify attendants at through points on the built-up connection that the telegraph connecting cord circuits per Fig. 2, which interconnects the line facilities such as Fig. 1 and 3 at the intermediate points should be disconnected. This is accomplished by operating key RING momentarily which applies i volts, 20-cycle signals via resistance 331 and back contacts 353 of relay Al to the ring conductor of the cord. These alternating voltages are applied through the line winding of relay S in the line repeater and cause the relay to respond and send out alternate mark and space pulses. 'Ihese pulses pass through the telegraph connecting cord circuit at each through point and light the locked-in supervisory lamp as previously discussed.

Cord CIS, relays SI, F, SQ, SP, A2 and R2, tube 332 and keys FDX-HDX and SPLIT serve no useful function when the cord circuit is connected to a KSP jack. These apparatus units function when the circuit per Fig. 4 functions with other circuits in the telegraph service board.

Fig. 5 is a diagram showing the relationship of Figs. 1 to 4 in a typical arrangement which should be understood from the foregoing. In this gure three service boards are shown interconnected by two telegraph channels each of which channels is terminated at each switchboard in a jack designated LEGS and in another designated KSP or communication spare. The channels and their' terminations, as explained in the foregoing, may be interconnected through their respective LEGS jacks to otherl channels to form a private line concentration group at each telegraph service board. Each of the present channels is equipped at each service .board with an individual hub-type telegraph repeaterV so that it may serve in such a concentration group. At times, when it is not employed as part of a hubtype concentration group, it is available for communication between the personnel at the switchboards. y

One channel may serve for communication between two switchboards or a number of switchboards in tandem may be interconnected by a number of channels. The manual telegraph cord per Fig. 4 is employed at each end of the connection for communication. In a tandem connection the manual telegraph cord per Fig. 4 is employed to receive the information necessary to establish the connection and the telegraph connecting cord is employed as a connecting and supervisory link only at the tandem points.

What is claimed is:

1. In a hub telegraph repeater system, a telegraph switchboard, a first and a second telegraph channel connected through a rst and a second individual hub-type telegraph repeater at said switchboard, means of access to each of said channels for connecting each of said channels to hub-type repeater concentration'groups at said switchboard at a rst time, a first telegraph cord connectable to each of said channels, said cord including telegraph communication means to enable an attendant at said switchboard to communicate over each of said channels preparatory to establishing a tandem connection through said channels, a second interconnecting cord devoid of said communication means, a tandem connection extending through said rst channel, said second cord and said second channel at a second time, a supervisory signal control and a supervisory signal both in said second cord, said control responsive to signals transmitted over either of said channels.

2. In a telegraph system, a telegraph switchboard having two telegraph channels terminated thereat, each of said channels individually equipped with a hub-type telegraph repeater to permit its connection into hub telegraph repeater concentration groups at a rst time, means at said switchboard for interconnecting said channels in a tandem connection extending through a plurality of switchboards at a second time, said means comprising a first telegraph cord, having switchboard attendant telegraph communication means therein, connectable to said channels individually for the transmission of information necessary to establish said tandem connection, said means comprising also a second patching cord having a supervisory signal, and a supervisory signal control responsive to supervisory signals transmitted over a channel in said tandem connection, said patching cord vinterconnecting said channels, said patching cord devoid of attendant telegraph communication means.

3. In a telegraph system, two telegraph channels each having an individual hub-type telegraph repeater, means of access to each of said channels at said switchboard for interconnecting said channels in hub-type concentration groups at said switchboard, a telegraph switchboard attendants communication cord including means for enabling an attendant at said switchboard to communicate over each of said channels separately preparatory to establishing a single tandem connection through said channels, a single patching cord connectable to each of said channels for serving as a link in said tandem connection, a supervisory signal and a supervisory signal control in said patching cord responsive to supervisory signals transmitted over said channel.

NIATTHEW R. PURVIS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,834,910 Blanton Dec. 1, 1931 1,835,549 Wishart Dec. 8, 1931 1,986,679 Lewis Jan. 1, 1935 2,173,551 Fitch Sept. 19, 1939 2,228,890 Singer Jan. 14, 1941 2,349,586 Bonorden et al. May 23, 1944 2,352,272 Large et al June 27, 1944 2,360,040 Dahlbom et al Oct. 10, 1944 2,464,371 Blyholder Mar. 15 1949 

